Organic Chapter 2: Alkanes & Halogenoalkanes Flashcards
What is the General Formula for an alkane?
CnH2n+2
What is an alkane?
A saturated hydrocarbon
What is the general formula for a Cycloalkane?
CnH2n
What is Crude Oil mostly made up of?
Alkanes
Why do we separate Crude Oil?
It’s not very useful in raw form
How do we separate Crude Oil?
Fractional Distillation
How does Fractional Distillation work?
Crude Oil is vaporised at around 350 degrees C
Vaporised Crude Oil goes to the top of the fractioning column
Crude Oil vapour gets cooler as it goes up the column
Each different chemical condenses at a different temperature - liquids get filtered off
Hydrocarbons with lowest & highest bp are taken at the top & bottom of the column respectively
How can you separate long chain hydrocarbons?
Cracking
What are the two types of Cracking?
Thermal Cracking
Catalytic Cracking
What are the conditions for Thermal Cracking? What does it mainly produce?
High pressure & High temp (up to 70atm & 1000 degrees C)
Produces a lot of alkenes
What are the conditions for Catalytic cracking? What does it mainly produce?
Takes place in the prescence of a Zeolite Catalyst at a slight pressure & high temperature (450 degrees)
Mostly produces aromatic compounds
Catalytic cracking is cheaper and faster.
What are alkanes useful for?
Fuels
What causes incomplete combustion?
Lack of oxygen
What is the equation for incomplete combustion of methane?
2CH4 + 3O2 -> 2CO + 4H2O
Why does burning fossil fuels contribute to global warming?
It produces carbon dioxide - this is a greenhouse gas.
What do Catalytic converters do on cars?
Remove unburnt hydrocarbons & oxides of nitrogen from the exhaust
What causes acid rain?
Sulfur Dioxide
What is a Free Radical?
A particle with an unpaired electron
What causes free radicals to form?
When a covalent bond splits equally - both atoms get 1 of the shared electrons
What is special about free radicals?
They’re very reactive due to the single unpaired electron
How do you indicate a free radical?
Dot next to the chemical
e.g Cl.
What is an initiation step?
A step in a reaction where free radicals are produced
What is a propagation step?
Free radicals are both used up & created
What is a termination step?
Free radicals are completely used up
Why are CFCs now banned?
Because they produced chlorine free radicals and caused ozone layer damage
What is the equation for chlorine free radicals breaking down the ozone layer?
Overall: 2O3 -> 3O2
Cl2 -> 2Cl.
Cl. + O3 -> O2 + ClO.
ClO. + O3 -> 2O2 + Cl.
2Cl. -> Cl2
Under what conditions do free radicals form?
Prescence of UV light
What is a Halogenoalkane?
An alkane with a halogen atom on it
What is special about the carbon-halogen bond in a halogenoalkane?
It’s polar
What are some nucleophiles that can react with halogenoalkanes?
OH-
CN-
NH3
What reaction do Halogenalkanes undergo to become alcohols?
Nucleophilic substitution
warm Aqueous sodium or potassium hydroxide
What reaction do Halogenoalkanes undergo to become Nitriles?
Nucleophilic substitution
Warmed ethanolic potassium cyanide
Heat under Reflux
What reaction do Halogenoalkanes undergo to become Amines?
Nucleophilic substitution
Excess Ethanolic Ammonia
Which Halogenoalkanes react the fastest and which the slowest?
Iodoalkanes are the fastest
Flouroalkanes are the slowest
What reaction do halogenoalkanes undergo to become Alkenes?
Elimination
Ethanolic hydroxide ions
Heat under reflux
